The present invention relates to a method and a device for triggering a solenoid valve, particularly for injecting fuel into an internal combustion engine.
German Patent Application Ser. No. 197 46 980 describes a method and a device for triggering a solenoid valve in which the triggering phase of the solenoid valve is subdivided into a pull-up phase and a holding phase. During the pull-up phase, a valve needle of the solenoid valve is caused to open by a first current intensity flowing through a magnetic coil of the solenoid valve. During the holding phase, the valve needle is held in the open state by a second, lower current intensity flowing through the magnetic coil. At least once at the beginning of the pull-up phase, a booster phase is activated during which a pulse-shaped booster current from a booster capacitor charted to a high voltage or from another current source flows through the magnetic coil.
FIGS. 1 and 2 show, in the form of signal diagrams, the characteristic of the voltage and of the current at and through, respectively, a magnetic coil of an injector during a triggering phase composed of a pull-up phase TA and a holding phase TH, and specifically, FIG. 1 for the case when the supply battery has a normal voltage level, e.g. UBATT=14 V, and FIG. 2 for the case when the supply battery has too low a voltage level of less than, for example, 14 V.
As shown in FIG. 1, after the initial current maximum IBOOST, caused by a first booster phase B1 with great booster voltage UBOOST, the current reaches a pull-up current level IA by which the valve needle of the solenoid valve is able to pull up. It is clear that booster voltage UBOOST, which is impressed on the solenoid valve during booster phase B1, is much greater than battery voltage UBATT. During pull-up phase TA, pull-up current level IA is regulated by repeatedly impressing battery voltage UBATT on the magnetic coil. Pull-up phase TA is followed initially by a brief free-running phase or a rapid extinction, during which the current through the magnetic coil of the injector decreases very rapidly and a holding-current level IH is reached which, during holding phase TH, is regulated to a setpoint level by repeated pulse-shaped impressing of battery voltage UBATT. At the end, following holding phase TH, there is again a free-running phase or rapid extinction, at whose end the current through the magnetic coil is completely decayed.
FIG. 2 shows the case when the valve needle is unable to pull up during pull-up phase TA because of too low a battery voltage UBATT2 (FIG. 2) less than UBATT (FIG. 1). Thus, particularly at low battery voltage accompanied by a given ohmic resistance in the circuit, sufficient pull-up current for the solenoid injection valve cannot be built up, that is to say, (I less than IA). FIG. 2 shows that current I through the magnetic coil falls off very rapidly and the regulating range of the pull-up current is not reached, and therefore reliable opening of the solenoid valve may no longer be ensured.
In order to achieve good dynamic response of the valve, the level of the current through the injector should remain at a high level as much as possible during the entire opening movement of the valve needle in pull-up phase TA. Because of the high withdrawal of energy from the internal booster capacitor, a theoretically conceivable, long booster phase producing this high current level over the entire pull-up phase may not be sensible. In realistic applications, the booster phase may be used to achieve a high current level as quickly as possible, a large portion of the booster energy being converted into eddy currents at the beginning of pull-up phase TA. Even before the valve needle is completely open, under certain operating conditions, booster phase B1 is broken off, the valve current is driven from the battery, and decreases. Thus, during the actual flight phase, which is the phase during which the valve needle moves, the magnetic force has already fallen again from its maximum value resulting in a poor dynamic response of the solenoid valve.
In view of the disadvantages of conventional methods described above, an object of the present invention is to utilize the booster energy economically and, in addition, to improve the switch-on performance of the valve, despite given a small battery voltage.
According to one aspect of the present invention, this object may be achieved by activating a plurality of booster pulses in succession during the triggering phase of the solenoid valve. In principle, their time position within the triggering phase may be freely selectable.
Thus, in a first exemplary embodiment of the present invention, after the first booster pulse is activated at the beginning of the pull-up phase, a further booster pulse can be activated still prior to or during the flight phase of the valve needle.
According to a second exemplary embodiment, after the first booster pulse is activated at the beginning of the pull-up phase, a further booster pulse can be activated at the end or immediately after the flight phase of the valve needle.
Finally, according to a third exemplary embodiment, a further booster pulse or a plurality of further booster pulses can be activated during the holding phase of the solenoid valve, if the voltage of the supply battery lies below a specific threshold voltage during this holding phase.
The exemplary embodiments of the present invention described above can also be combined with one another.
The energy or the maximum current of the individual booster pulses can be reduced by the repeated boosting compared to one long single boosting with a very high current intensity. A reduced peak current intensity may result in a lower load of the bonding pads for integrated circuits, of hybrid assemblies, and a smaller storage capacitance of the booster capacitor.
By suitable selection of the moments for the second and possibly third booster pulse, the buildup of the magnetic force can be freely varied timewise. This leads to a decrease in the eddy-current formation, and booster energy can be supplied depending on the need of the solenoid valve as a function of time. In this manner, the pull-up movement of the valve needle away from the lower limit-stop point can be supported, the needle flight can be accelerated, and stop bounces at the upper limit stop of the valve needle can be suppressed.
Furthermore, given too low a battery voltage which may not be enough to drive a sufficiently high current through the high-pressure injector, the current level can nevertheless be raised by the multiple boosting, and thus reliable operation of the high-pressure solenoid injection valve can be ensured.